1. Field of the Invention
This invention relates to an improved circuit interrupting device, and, more specifically, relates to a simple, inexpensive circuit interrupting device which is bus-mountable and manually resettable and which is simple in construction and reliable in operation.
2. Prior Art
Various types of circuit interrupting devices--including fuses or fuse-like devices, circuit breakers, reclosers, and Circuit Switchers--are well known for circuit protection. These devices have varying operational characteristics and features which make their use attractive in some environments, but less attractive in other environments. In the past, operational features tended to be the sole criterion determining which type of device was to be used. Today, however, the cost of the devices is becoming an important, if not the most important, determinant relative to deciding which device shall be used in a particular environment. Users of circuit interrupting devices are often willing to forego purchasing expensive, exotic, full-range interrupting capability devices and to purchase less expensive, simpler devices, even though the latter may have more limited interrupting capabilities.
One use environment in which users today may employ less expensive, simpler devices is transformer protection. Devices which up to now have been employed for transformer protection have been either complicated or expensive or both. Economic conditions have forced equipment users, especially utilities, to consider employing transformer protective devices which are not full range and are less versatile or sophisticated, but which are, at the same time, substantially less expensive. Specifically, many utilities have come to realize that there are times when it is expeditious to use an inexpensive interrupting device having a more limited interrupting rating as opposed to a full-range interrupting device, if the inexpensive device is sufficiently less expensive than alternative full-range devices so as to make the use of the former attractive from a capital investment standpoint.
Most prior art interrupting devices include various types of "intelligence" and sensors. The intelligence processes information provided by the sensors, which information relates to the current in an electrical circuit. The intelligence dictates the operation or lack of operation of the device based on such information. Various sensing and intelligence schemes are well known; some are simple, while others are quite complex. One common characteristic of most present-day transformer protective devices is the location of the sensing and/or intelligence at ground potential rather than at line potential. This location, of course, necessitates electrical insulation and isolation between the sensing and intelligence, on the one hand, and the device at line potential, on the other hand. This requirement for isolation in turn leads to the use of complex mechanical and electrical schemes for interconnecting the sensing and the intelligence, which are at ground potential, to the circuit interrupting device, which is at line potential.
Accordingly, it is desirable to provide a simple, reliable, inexpensive interrupting device having a limited interrupting rating, but which nevertheless is attractive in view of its low cost. It is also desirable to provide a device which is completely bus- or line-mountable and which operates at bus or line voltage. Such a device is even more attractive should its entire sensing and intelligence also be at line or bus potential, thus obviating the need for complex interconnections between the interrupting device and the intelligence and sensing. From a cost standpoint, it would also be desirable to have such a device manually resettable from the ground level which, accordingly, obviates the necessity of an expensive and complicated reclosing mechanism. Toward these ends, the present invention is aimed.